Hierarchical storage management (HSM) is a technique for managing files in appropriate storage devices (storage units) in accordance with a predetermined rule (policy. HSM is a technique in which a plurality of storage units, such as an SSD (Solid State Drive), an HDD (Hard Disk Drive), and a magnetic tape medium (tape medium), for example, are arranged into a hierarchy, and data is moved within the hierarchy on a per file basis.
In HSM, a file on a higher level, such as a file on an HDD, for example, is moved to a lower level, such as a tape medium, in accordance with access frequency and file type when storage usage exceeds a threshold, for example.